Set up a total surveillance state (or exploit an existing one), reducing any notion of privacy to zero including privacy of thought;

Force merger (cyborgization) by requiring that all people have a brain implant which allows for direct mind control/override by the superintelligence;

Enslave humankind, meaning restricting our freedom to move or otherwise choose what to do with our bodies and minds. This can be accomplished through forced cryonics or concentration camps;

Abuse and torture humankind with perfect insight into our physiology to maximize amount of physical or emotional pain, perhaps combining it with a simulated model of us to make the process infinitely long;

Commit specicide against humankind, arguably the worst option for humans as it can’t be undone;

Destroy/irreversibly change the planet, a significant portion of the Solar system, or even the universe;

Unknown Unknowns. Given that a superintelligence is capable of inventing dangers we are not capable of predicting, there is room for something much worse but which at this time has not been invented.

(Having blogged that, I'm with Darius on this one: „I find AI optimists to be about as frustrating as AI pessimists. My position: AI is weird! Really fucking weird!!“)